1. Field of the Invention
The present invention relates to bottom hole drilling assemblies and, more particularly, to bottom hole drilling assemblies connectable to coiled tubing and used for directional drilling.
2. Description of Related Art
With the decline of oil production from existing wells in certain areas of the world, there has arisen in the oil production industry a recognition of the benefits of reentering existing wells and drilling lateral well bores out therefrom. These lateral well bores will, hopefully, increase the recovery rates and increase the quantity of oil recovered from these wells. Typically, these reentry drilling operations utilize downhole motors and electric steering tools to allow the drilling operator to properly guide or "steer" the path of the drill string as it creates the new, lateral well bore.
Several disadvantages of the above described reentry drilling operation have become apparent, and these include the relatively high cost of a workover rig, especially for offshore operations, and the need to drill "over pressure", i.e. to stop the flow of fluids from the subterranean formations while drilling. As has been found in re-entry drilling operations, such over pressuring can severally damage certain formations, which cause the quantity of oil recovered therefrom to sharply decrease.
In recent years the use of coiled tubing for drilling has increased due to the lower cost of a coiled tubing unit versus a conventional workover rig, and the ability of coiled tubing to drill while the well bore is "under pressured", i.e. the flow well bore fluids are not stopped while drilling. An example of a coiled tubing drilling unit and related methods of drilling with coiled tubing are described in U.S. Pat. No. 5,215,151, which is incorporated herein by reference.
Unfortunately, several disadvantages have become apparent in the use of the above described coiled tubing drilling operations. These disadvantages include: (i) the inability of the coiled tubing to be pushed from the earth's surface very far out into the formation before it buckles, and (ii) the inability of the coiled tubing to resist reactive torque of the downhole motor which can twist and kink the coiled tubing.
There is a need for a simple coiled tubing drilling assembly and related methods of use that can cost effectively drill a curved bore hole of any desired inclination and minimize bucking and twisting of the coiled tubing as the bore hole is extended laterally out from an existing well bore.